This invention generally relates to golf balls with high coefficient of restitution, and more particularly to a low deformation golf ball at high club speeds.
Golf balls have been designed to provide particular playing characteristics. These characteristics generally include initial ball velocity, coefficient of restitution (CoR), compression, weight distribution and spin of the golf ball, which can be optimized for various types of players.
Golf balls can generally be divided into two classes: solid and wound. Solid golf balls include single-layer, dual-layer (i.e., solid core and a cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by tensioned elastomeric thread, and a cover.
Generally, if a dual-layer solid golf ball has a soft core and a hard cover, it has a low spin rate. If the solid golf ball has a hard core and a hard cover, it exhibits very high resiliency for distance but has a xe2x80x9chardxe2x80x9d feel, and is difficult to control on the greens. Additionally, if the golf ball has a hard core and a soft cover, it will have a high rate of spin. More recently developed solid balls have a core, at least one intermediate layer, and a cover. The intermediate layers improve the playing characteristics of solid balls, and can be made from thermoset or thermoplastic materials. In an effort to improve various properties of golf balls further, symmetrical, non-spherical cores and core layer have been contemplated in the patent literature.
Several patents are directed to inner cores that have been modified with non-spherical features such as bores or projections.
U.S. Pat. No. 720,852 issued to Smith discloses an internal core with small, solid protuberances projecting therefrom. The core is encased in a rubber layer having small, solid protuberances projecting therefrom. A silk layer is wound thereto, and then the ball is encased in an outer covering. The non-spherical core protuberances anchor the rubber and silk layers and increase the resiliency of the ball as a whole.
U.S. Pat. No. 1,524,171 issued to Chatfield discloses a core with a hollow, spherical center that supports cylindrical, solid lugs. A spherical casing surrounds and abuts the tips of the lugs. The lugs and casing are designed so that the casing compresses the lugs in the finished ball. Fluid or wound rubber bands occupy the space around the lugs, between the spherical center and the casing. The non-spherical lugs promote the accurate location of the center by facilitating uniform and spherical winding of the rubber bands about the center. An outer shell surrounds the casing.
U.K. Patent Application No. 2,162,072 issued to Slater discloses a golf ball with a non-spherical inner core that includes solid, support members or struts that diverge from a common center. The struts form a generally cubic, tetrahedral, or octahedral shaped core. The struts locate the inner core symmetrically within a mold cavity. An outer core is molded about the inner core, and a cover is molded thereon. The inner and outer cores are formed from identical or similar materials.
U.S. Pat. No. 5,480,143 issued to McMurry discloses a substantially spherical practice ball comprising mutually perpendicular members with a plurality of walls that interconnect the members. The walls increase the drag on the ball so that smaller playing fields can be used.
U.S. Pat. No. 5,836,834 issued to Masutani et al. discloses a two or three-piece golf ball comprising a two-layer solid core composed of a low-hardness inner core and a high-hardness outer core joined around the low-hardness inner core. A projection is formed on the inner surface of the high-hardness outer core such that the projection extends along an approximate normal direction, while a depression corresponding to the projection is formed in the outer surface of the low-hardness inner core, and the low-hardness inner core and the high-hardness outer core are joined together such that the projection is inserted into the depression.
Other patents disclose adding perimeter weights to golf balls to increase its moment of inertia. U.S. Pat. No. 5,984,806 discloses a golf ball with visible perimeter weights disposed on a spherical inner cover.
However, the prior art does not contemplate using non-spherical cores to improve the CoR of golf balls.
Hence, the invention is directed to a golf ball having core geometry designed to provide improved playing characteristics such as coefficient of restitution.
The invention is also directed to provide a golf ball having an inner core that comprises a pre-formed non-spherical core insert or inner core.
These and other objects of the present invention are realized by a golf ball comprising a core, which comprises a pre-formed non-spherical insert embedded within a polymeric core material and is encased by a cover. The golf ball has a coefficient of restitution of at least 0.810 at a collision speed of about 125 feet per second or higher. Preferably, the coefficient of restitution is at least 0.790 at collision speed of about 140 feet per second or higher, and more preferably the coefficient of restitution is at least 0.760 at collision speed of about 160 feet per second or higher.
In accordance to another aspect of the invention, the golf ball has a first coefficient of restitution of at least 0.810 at a collision speed of about 160 feet per second or higher against a flexible impact surface, wherein the impact surface has a second coefficient of restitution of about 0.830.
The pre-formed non-spherical insert has a flexural modulus in the range of about 25,000 psi to about 250,000 psi. More preferably, the pre-formed non-spherical insert has a flexural modulus in the range of about 75,000 psi to about 225,000 psi, and most preferably the pre-formed non-spherical insert has a flexural modulus in the range of about 80,000 psi to about 200,000 psi.
Furthermore, the flexural modulus of the polymeric core material is at least about 500 psi less than the flexural modulus of the pre-formed non-spherical insert. Preferably, the flexural modulus of the polymeric core material is at least about 1000 psi less than the flexural modulus of the pre-formed non-spherical insert. More preferably, the flexural modulus of the polymeric core material is about 20,000 psi to about 50,000 psi less than the flexural modulus of the pre-formed non-spherical insert. Most preferably, the flexural modulus of the polymeric core material is at least about 100,000 psi less than the flexural modulus of the pre-formed non-spherical insert.
In accordance to another aspect of the invention, the pre-formed non-spherical insert has compression in the range of about 50 Atti to about 120 Atti. Preferably, the pre-formed non-spherical insert has compression in the range of about 60 Atti to about 110 Atti. More preferably, the pre-formed non-spherical insert has compression in the range of about 80 Atti to about 100 Atti.
Furthermore, the compression of the polymeric core material is about 5 to 100 Atti less than the compression of the pre-formed non-spherical insert. Preferably, the compression of the polymeric core material is about 20 to 80 Atti less than the compression of the pre-formed non-spherical insert. More preferably, the compression of the polymeric core material is about 30 to 60 Atti less than the compression of the pre-formed non-spherical insert.
In accordance to another aspect of the present invention, the pre-formed non-spherical insert has a hardness of greater than about 40 Shore D. Preferably, the preformed non-spherical insert has a hardness of greater than about 60 Shore D. More preferably, the pre-formed non-spherical insert has a hardness of greater than about 65 Shore D. Furthermore, the hardness of the polymeric material is at least about 1 Shore D less than the hardness of the insert.
In accordance to one aspect of the invention, the preformed non-spherical insert is symmetrical, and comprises a central portion and a plurality of projections. The projections comprise a substantially conical head disposed at the distal end of each projection. The outermost surfaces of the conical heads lie on a spherical surface. The projections are separated by predetermined gaps.
In accordance to another aspect of the present invention, the insert comprises a plurality of connected rods and a plurality of balls disposed at the distal ends of the rods. Alternatively, the balls may assume mushroom or anchor shape. Furthermore, the insert further comprises a hub connected to the rods.
In accordance to another aspect of the present invention, the insert comprises a plurality of interconnected rings and/or a center. Alternatively, the insert comprises a plurality of interconnected disks. Furthermore, the insert may comprise a hollow shell having openings on its surface. The shell may comprise rigid chambers on its surface, which may have a center hub connected to the shells by rods.